Car sales may be picking up, but Americans are driving less and less each year.

According to the latest U.S. Department of Transportation data, travel on all roads and streets dropped 1.4 percent in February 2013 (PDF), compared with February 2012—the equivalent of roughly 3.1 billion miles. Meanwhile, cumulative travel for 2013 dropped 0.4 percent, or 1.8 billion miles.

The slowdown looks more dramatic when you go back a few years and adjust for population growth. Doug Short, vice president of research at Advisor Perspectives does just that in a series of charts released earlier this week. One of his graphs, which uses U.S. Bureau of Labor Statistics data to account for population growth, shows that the estimated miles driven on all U.S. roads has plunged 8.75 percent since June 2005.

So why are Americans driving less each year? Historical perspective indicates that the recession can’t be the only cause. “This isn’t the first time Americans have pared back their driving habits,” writes Brad Plummer of the Washington Post. ”After the OPEC oil shock in the late 1970s, miles driven fell about 6 percent from the peak, though they started climbing again by the end of the recession in 1982.” So far, the current economic recovery has not led to more driving.

Volatile gasoline prices are a possible factor, though Short notes that the correlation between miles driven and gasoline prices is actually quite weak. “There are profound behavioral issues apart from gasoline prices that are influencing miles driven,” he wrote. “These would include the demographics of an aging population in which older people drive less, continuing high unemployment, and the ever-growing ability to work remote in the era of the Internet.”

There has also been a startling drop-off in the car culture of American youth: “From 2001 to 2009, the average annual number of vehicle-miles traveled by young people (16 to 34-year-olds) decreased from 10,300 miles to 7,900 miles per capita—a drop of 23 percent,” reads a Frontier Group study published last April.

The same study also outlines other telling trends. From 2001 to 2009, 16- to 34-year-olds took 24 percent more bike trips and were 16 percent more likely to walk to their destinations. Meanwhile, from 2000 to 2010, the share of 14- to 34-year-olds without drivers’ licenses increased from 21 percent to 26 percent. Many young people now prefer to live where they can walk, bike, or take public transportation. Some are ditching cars for environmental reasons. Other contributing factors may include improved public transportation, as well as laws that make it more difficult to obtain a driver’s license.

There’s also the possibility that young people just aren’t getting out as much. According to Frontier Group, “Communications technology, which provides young people with new social-networking and recreational possibilities, has become a substitute for some car trips.”

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